Coverage.py works well, and I want it to properly measure any Python program,
but there are some situations it can’t cope with. This page details some known
problems, with possible courses of action, and links to coverage.py bug reports
with more information.

I would love to hear from you if you have information about
any of these problems, even just to explain to me why you want them to start
working properly.

If your problem isn’t discussed here, you can of course search the coverage.py
bug tracker directly to see if there is some mention of it.

There are a number of popular modules, packages, and libraries that prevent
coverage.py from working properly:

execv, or one of its variants. These end the current program and replace
it with a new one. This doesn’t save the collected coverage data, so your
program that calls execv will not be fully measured. A patch for coverage.py
is in issue 43.

thread, in the Python standard library, is the low-level threading
interface. Threads created with this module will not be traced. Use the
higher-level threading module instead.

sys.settrace is the Python feature that coverage.py uses to see what’s
happening in your program. If another part of your program is using
sys.settrace, then it will conflict with coverage.py, and it won’t be
measured properly.